Radiofrequency circuits



Jan. 6, 1931. L. L. JONES RADIOFREQUENCY CIRCUITS 2 Shuts-Sheet 1 Filed Oct'. 5, 1929 INVENTOR v Leshzr L. Jones A ORNEYS Patented Jan.'6,.1931 I I a p f UNITED" STATES PATENT OFFICE LESTER- L. JONES, F ORADELL, NEW JERSEY RADIOFREQUENCY' CIRCUITS: Application filed October 5, 1929. Serial No. 397,632.

This invention relates to radio frequency than the highest frequency of the Working circuits and more particularly to coupling; frequency range in Whichthe circuit is to be means for successive vacuum tubes employed employed. The output circuit is therefore in radio receiving circuits. always inductive and therefore always regen- In my copending application, Ser. No. erative. 205,934, filed July 15, 1927, since issued on To counteract for this regenerative effect July 15,1930, as Patent No. 1,770,525, I have suitable neutralizing means may be emdisclosed a radio receiving circuit comprising ployed, which preferably may take the form a selector or tuning means having variable of a resistance 8, which is desirably made circuit constants followed by a vacuum tube capacitance and inductance free, and of ap-' amplifier having fixed circuit constants, and propriate magnitude to cause a feed ,for-' a coupling means therein arranged to prevent ward current through the tube 2 which opreaction by the amplifier on the selector. The poses and neutralizes the regenerative feed primary object of my .present invention is to back current, all as has been set forth more 15 improve such reactionless coupling means in d ail in my U. S. Patent No. 1,713,130

used between any successive vacuum tubes, I d ay 14,1929. and more especially to improve the coupling. AS in h Case Of h Circuit t forth in means used in a radio receiving circuit such my copending application, Ser. No. 205,934, as is disclosed in the said copending applicady e erred to, the succeeding vacuum 20. i tube 10 is coupled to the output circuit of the 7 0 To the accomplishment of the foregoing Vacuumtube 2 through a capacitance and such other objects as will hereinafter apl2 and an inductance 14, the coupling inpear, my invention consists in the circuit eleductance 14 being connected across thements and their relation one to the other as cathode and control electrode of the tube 10,

hereinafter .are more particularly describedand serving incidentally todetermine the 7 in the specification and sought to be defined bias potential thereof, while the capacitance in the claims. The specification is accom- 12 is connected between the output circuit of panied by drawings in which: 1 the tube 2 and the control electrode of the Fig. 1 illustrates my invention applied to tube 1.0. The capacitance 12 and inductance impedance coupled tubes; g 14 are preferably so dimensioned as to be se- Fig. 2 illustrates the invention applied to ries resonant to a, frequency lower than the transformer coupled tubes; lowest frequency of the working frequency Fig. 3is amodification ofthe arrangement range, whereby there is a tendency to inshown in Fig.2; crease 'the amplification of the lower fre- 35 Fig. 4 is a series of graphs explanatory of 'quency signals.

my invention; When only a'single tube as, for example, Fig. 5 is a schematic wiring diagram for a the tube 2 so far described, i's used as a re-" radio receiving circuit embodying my invenactionless link the tube is relatively jineifi tion'; and cient as an amplifier stage. This iss'o be-- 40 Fig. 6 is a schematic wiring diagram for a cause the preferably capacitance and induct different receiver circui further embodying .tance free resistance 8 is given a magnitude my invention. approxirnately equal to the impedance of the Referring to Fig. 1, which is a fragmentary tube divided by the amplification constant portion of a complete Wiring diagram, it will thereof, as is explained in my Patents Nos. 45 be observed that the anode 4' of a vacuum 1,713,130 and 1,713,132. The, resistance tube2 is connected to a source of anode curtherefore is only of the order'of a thousand sc -eat" through an inductance 6.- This inducto two thousand ohms in the case of ordinary tance is of such magnitude and constructionl present day amplifier tubes, for example, that it causes the output circuit of the tube tubes of the 227 type having an inter-electo be naturally resonant to a frequency higher trode capacltance of the ord'erof-three M. '1

than the highest frequencyfo'f the'fwo'rking frequency range. The foregoing relative values of inductance and resistance may, of course, be slightly varied to more accurately balance the feed back" reaction due to the induct-ance and the feed forward reaction due to the resistance. Now, while such a reactionless stage is workable it is not as efliclent an amplifier stage as might be desired bccause-the total impedance in the output circuit is only a fraction of the tube impedance instead of being equal to or larger than the tube impedance, as it should be for maximum amplification.

Furthermore, when a reactive load is coupled to the output circuit its upsets the balance of reactions, and to overcome this by the method taught in my Patent No. 1,020,661,

issued March 15, 1927, by tapping the succeeding circuit into the resistance at an intermediate point thereof such that feed forquits.

ward and feed back reactions are balanced, still further reduces the amplification owing to the resulting reduced coupling obtained 'between the output and the succeeding cir- In order to increase the gain obtainable I first couple the succeeding circuit to vthe plate end, of the resistance, thereby obtaining the maximum coupling between the circuits.

But of greater importance, raise the gain obtainable in the transition or reactionless link tube 2 I find it feasible to increase by approximately two-fold the re sistance and inductance values suggested above, the resistance. then being of theorder of 2800 ohms, and the inductance being-of the order of 230 microh. This approximatelydoubles the impedance of the output circuit and approximately doubles the gain in the tube. f

To explain this more in detail, the desired resonance frequency may be obtained by either a relatively large inductance in parallel with a. relatively small capacitance or a relti-vely small inductance 'inparallel with a relatively large capacitance. I intentionally select a large inductance, and to make this possible intentionally reduce the capacitance in parallel therewith. This capacitance'may be reduced. first,'by the use of tubes having a low inter-electrode tube capacitance, and sec- 0nd, by reducing theexternal capacitance by refinements in the construction of the apparatus, such as the use of short leads, the reduction in area and linear dimension of the resistance 8 and the capacitance 1G, and the in order to 'outputcircuit impedance at frequencies in the working frequency range and this results in better amplification. The larger output inductance incidentally causes augmented feed back which necessitates a larger resistance in order to obtain augmented feed forward energy, for opposing the feed back energy. The increased magnitude of the feed forward resistance 8 also increases the impedance of the output circuit of the tube, and therefore also leads to better amplification. The capacitance necessarily hanging onto the anode end of the output circuit causcs feed forward and damping or degeneration, to avoid which the resistance 8 may be increased slightly less than proportionally to the increase in inductance 6.

.lVhen the above changes for higher efficiency amplification are made there still appear in the input circuit of the tube slight variations from the zero reaction condition. The major of these variations is a tendency toward regenerative feed back on low frequencies, and damping or feed forward on high frequencies. This can be generally corrected by causing a decreasing capacitance from plate to ground with increasing frequency This is accomplished. as has already been explained in my copending application, Scr. No. 205,934, since issued as Patent No. 1,770,-

525, already referred to, by suitably arranging the output circuit of the following tube although the specific quantitative dimensions there given differ somewhat, being applicable to tubes of the 201A type, having an amplification constant of approximately 8, an inter-electrode tube capitance of approximate- 1y 8 11. M. F., and a tube impedance of approximately 8000 ohms.

Tube 10 in 1 has connected in series with its anode an inductance 11 which is a relatively-large inductance, so dimensioned as to be naturally resonant, together with the capacitance hanging thereon, to a frequency lower than the working frequency range. I

If it is the primary of a transformer, as is usually the case, the transformer should preferably be bifilar ,wound. The working frequencies are then higher than the resonant frequency, and forthese frequencies the outi put circ'uitis effectively capacitive, and therefore is of decreasing impedance with increas- 1 ing frequency, which causes a decreasing ap-. parent nput capacitancewith increasingfrequency. The capacitance therefore varies in opposite sense to the frequency and in the capacitance of tube is transferred directly to the output circuit of tube 2 by the coupling means therebetween, and the said capacitance alters the constants of the output circuit of tube 2 in the proper direction to correct for the major residual or disturbing reactions caused by the increase in the inductance 6 and resistance 8 of the output circuit of tube 2 above the values specified in my aforesaid patents to prevent reaction through the tube. There still remain minor variations, with which I shall next deal.

One of, such minor variations is a tendency toward regenerative feed back in the middle of the working frequency hand. To correct this, in accordance with my present invention a capacitance 16 is arranged in shunt or parallel with the feed forward resistance 8, and this capacitance I have empirically found serves thefunction of causing a decreased regenerative action in the middle of the band. Its advantages are particularly applicable to a vacuum tube amplifier, preceded by a very sharply tuned circuit, the condenser 16 serving to make the effect of the reaction of the amplifier on the sharply tuned circuit more nearly like that of a fixed loss free condenser of small capacitance. D

As stated, without the fixed condenser 16 the input characteristic of the tube'usually shows a regenerative tendency in the middle of the working frequency band. The magnitude of this tendency is generally of such an order as would decrease the-damping of the sharply-tuned input circuit to'one half of itsnormal damping when all the constants are set so as to provide for the absence of reaction at the upper and lower extremes of the working frequency band. The addition of the condenser 16 permits of the elimination of this slight regenerative tendency without any appreciable sacrifice of gain and without the introduction of any'other operating disadvantage.

In Fig. 2' I have illustrated a modified form of the invention which employs transformer coupling between stages, and which possesses certain advantages for that reason.

One of these is that the elimination of the condenser 12 eliminates a art having a high capacitance to ground an therefore reduces the capacity shunt across theoutput circuit of the tube and so improves the efiiciency thereof, a bifilar wound transformer being no worse than asingle inductance as regards its capacitance to ground. Another advantage of the transformer coupling is that thecircuit may he built more compactly. A third advantage of the transformer coupling resides in the fact that it. provides a low resistance shunt path around the output circuit through which the steady component of the plate current may how even though the inductance of the transformer is so great relative. to the output inductance 6 that the 16 is added it becomes possible to increase the value of the resistance 8 to a value approximately twice the value above defined, Without introducing any appreciable reacvtion in the tube. This increases the imped ance of the output circuit and therefore inso creases the amplification gain.

It is generallyadvantageous in this class of amplifier to use tubes having relatively low output impedance. These tubes draw considerable plate current. It therefore follows that with the augmented value of resistance 8 there is a considerablepower loss in the series resistor as well as a fair voltage drop so that a slight loss .of amplification results due to the lower average potential on the plate.

The aforesaid third advantage of the transformer coupled arrangement is that it makes possible the provision of a low resistance shunt path around the series resistance 8 and impedance 6, through which the constant component-of plate current-can flow. This substantially eliminates the above described energy loss and voltage drop in the plate circuit, and thereby tends toslightly increase the amplification obtained as well as to provide greater freedom in the choice of the resistor 8. By this I mean that this resistor may thereby be made physically smaller, since there is no appreciable-power dissipation to be taken care of, and this, in

turn, further reduces the inherent capacity shunt across the output of they tube, thereby increasing its efliciency.

A fourth advantage of the transformer I coupled arrangement is that the inductance thereof may be optionally selected over a very \wide range, and it is therefore quite simple to choose for its inductance a value which will be suitably related to the apparent inputcapacitance of the following .tube, and to the changing capacitance'there obtained, to result in a helpful amount of automatic tuni. g of the input circuit of the following tube. A fifth advantage is peculiar to the use of a bifilar transformer or its equivalent, that is, a unity coupling or very-closely coupled transformer, and resides in the fact that such a'transformer transfers the changes in input capacitance of the following tube directly across to the output circuit of the preceding or link tube, and therefore is ideally suited for correcting the residual reaction which it has already been explained tends to arise a tube 10. Across the primary of the transance 8, and that the output fromtube 2 is Mranged n series with a capacitance and a tormer coupling, as in Fig. 2, is additionall former 20 there is connected a shunt circuit.

consisting of a resistance 8 connected in series with an inductance 6, while a capacitance 16 is arranged in parallel with the'resistance 8. Inductance 11 corresponds to inductance 11 in F 1.

In one aspect we may say that the output .circuitol the tube 2. in both Fig. l and Fig. 2, consists of an .inductance 6 of suitable dimension and construction to cause the reaction of the tube .in the. working frequency range always to be regenerative, together w th a neutralizing or feed forward. resistfed to a succeeding tube 10 through the coupling circuit 12, v14:, in Fi 1, or the transformer 20, in Fig. 2, while the operating and reactional characterlstics of the. circuit are improved by the addition of a capacitance 16 arranged in shunt with the resistance 8. In another aspect it' maybe statc d ,"bo'th with respect to the arrangements shown in Fig. 1

and Fig. 2, that the coupling n'lea -nsbetween successive vacuum tube 'stages,*wh1ch may beimpedance coupling,'as in Fig. 1, or transprovided with .a complex shunt c1rcu1t,;sa'i(lshunt ci-rcuit consisting of an inductance ar parallel connected resistance. Ibelieve thefirst viewpoint is the more correct ,-technically, and betterexplanatory of the operation of the circuit. f

The arrangement shown in Fig. 3 correa sponds very closely with that shown in Fig. 2 except for the fact that the lower terminal 18 of the resistance 8 in this case is connected at an intermediate point on the inductance "6. that is to say, the resistance 8, instead of being connected in parallel with the capacitancc 16 alone, is'connected in parallel with the capacitance 16 and a port'ion of the inductance 6. This alteration is a further'retinement the use of which is optional, and the function of which will be explained in connection with the graphs shown in Fig. 4 of the drawin a f In order to determ ne the character of the reaction of an amplifier embodying the. foregoing coupling circuits I have found it convenient to usea method in which a simple sharply tuned circuit is used as a standard of comparison. For this purpose constant ire:

qu'ency energy is supplied from a source through a very loose coupling to such a'sha-rply resonant circuit, and at any given freing,

quency the amountof detuning needed to reduce the voltage across the resonant circuit alone to half of its maximum value is obtained. The curve D in Fig. 4 is a curve plotting these values, that is to say, the number of .M..M. F.s detuning needed to reduce the voltage across the resonant circuit to half its value plotted'as a function of wave length. Curve E is a curve arbitrarily obtained from curve'D. by making each ordinate half of the value-that it has in curve I). The region between-the curves D and l) is a region in which the'chai'acteristic of a commercial broadcast receiving amplifier sho'n-ld lie it best results are to be obtained.

The region above curve I) represents broader tuning, or increased dampin equivalent to the introduction of more resistance in the tuned circuit. The region below curve 1) represents sharper tuning, or decreased dampor the introduction of negative resistance into the circuit. If the circuit has an ideally efficient coil it would, of course. be desirable to approximate curve I). rather than to come in the region below curve I). The present specification that the curve fall in the region below curVeD is based upon the assumption that the coil is not ideal. nor even as good as may soon be approached as design and manufacture improves, and it is therefore preferred that the departure from curve D, if any, be in the direction of a more selective circuit equivalent to the use'of a more efiicient coil, but within the limit specified o' prevent instability.

"Essentially, what is desired is that the reactionless stage should be equivalent in its effect on the resonant circuit to a small pure and constant capacitance. It should be a pure capacitance in order to avoid changes in the sharpness of tuning in the resonant. circuit by the introduction of positive or negative resistance, except for the introduction of a slight negative resistance within the limit previously defined. This requirenu-nl is doubly important because the renction ali'ccls not only the last tuned circuit, when a selector consisting of tuned circuits cascaded directly together is employed, but also the prior tuned circuits, because, for example. the coupling thereb etween must be increased it resistance is introduced into one of the later circuits, and this broadens the tuning of all oi the circuits. The capacitance must be. constant so that the last circuit may be tuned toc'ether with-the preceding tuned circuits. The capacitance. must be small in order not to diminish the tuning range available with a' given variable condenser.

To determine the effect of coupling the am- .plifier, including the reactionless or transition "stages 2 and 10, upon the sharply tuned cir cuit, Iproceed as follows:

The'amphfier belng investigated is connected to the said. resonant circuit and the l ul * detuning needed to obtain half the maximum acteristic' curve for the tuned circuit when working into the amplifier lies above the voltage is again ascertained. If the charregien between the curves D and E a receiver embodying the circuits would tune broadly, and interference would tend to increase. If the curve liesbelow the region defined between the curves D and E-the receiver would tend to tune-too sharply,-and wouldbe apt J p to be too critical in operation and to lead to distortion by selectively amplifying the carrier and side band frequencies within the modulation range, andin extreme cases=to lead to oscillation. p i

Suppose now that the inductance 6 and resistance-$ yebeen substantially increased in magnitudeE'an'd 'thattheir relative magnitudes haveibeeni adjusted for: neutralizationwhen no succeeding circuiti s,.hung onto the output circuit of tube 2. A's' is explained in;'

ously-jmensi' my Patent'No. 1,620,661, 12 evi tioned, if a capacitance is hung oiito the audits terminal of resistance 8 there. is increased feed forward through the tube and c'onse-fl; quently increaseddegeneration or damping. If a capacitance is hung at the other terminal of the resistance 8 there is increased feed back and consequent regeneration. An. intermediate point may be selected for neutralization, but such neutralization is not accurate over thewave length band when the inductance 6 .llld resistance 8. have been greatly increased in impedance, and furthermore, the coupling to the succeeding tube 10 is inefficient because only a portion of the potential across the impedance of the output circuit of tube 2 is applied to the input circuit of tube .10.

I therefore prefer to couple the input circuit of tube -10 to the anode terminal ofthe resistance 8. This causes'fe'ed forward and damping in the input circuit of tube 2 and results in a reaction curve such asthe dotted curve F in Fig. '4. This curve. it will be observed, lies above curves D and E, showing the broadness of the resonance curve ofthe tuned circuit, or the increased damping caused by the capacitive .load on the anode terminal of resistance 8, Some capacitive shunting of the output circuit of tube 2 is inevitable, and for this reason I prefer as a generation, but this cannot be cured-simply by again partially increasing resistance 8 for moredegeneration, because curve G at the high frequencies already lies above curves D and E, and therefore. this region already has degeneration.

- It is obviousfrom'an inspection of both curve F and curve G that the real difiiculty' 18 that the-slope of the reaction curve, when a constant capacitance is hung onto the output circuit of tube 2, differs from theslope of the desired reaction curve. By loading a; variable capacitance onto the output circuit of tube 2- and making this capacitance increase at the low frequencies increasedwhimping may there be. obtained, as is desired, and by making this capacitance de-' crease at the high frequencies increased regeneration may there be obtained,"as is also desired in order to change the slope of curve -To this end the output circuit of tube 10 is made naturally resonant to a frequency lower than the working frequency range.

This circuit is therefore capacitive for fre- 'quencies in the working frequency range, and

frequency. This, in turn, causes diminishing gain in tube 10 with increasing frequency which, in turn, causes diminishing apparent input capacitance in tube 10 with increasing frequency. This variation is in the proper sense to correct the slope of curve G, and the range of variation may be controlled, but the nature or rate of variation throughout the range cannotbe exactly controlled. Asa result areaction curve like the dotted-curve A in Fig. 4 is obtained. It will be observed that the general or average slope of curve A isabout what is desired, but that the curvature differs from the desired curvature,-for the curve A shows a regenerative tendency in the middle of. the frequency range.

By adding the condenser 16 in the manner shown in Fig. 1 or in Fig. 2 the curve B is obtained, and this, it willbe observed, is a great improvement, for the curve is fairly regular throughout most of its range and is generally similar in configuration to the curves D-and E, as well as lying therebetween; However, this curve has anundesirable irregularity near the shorter wave length end of the range, 'sa at250 meters, and it is. with a view to obviateeven'this minor defeet that the arrangement shown in Fig. 3 may be employed. The latter arrangement results'in a curve like the curve C,,which obviously fulfills all that is to be expected and desired. If the amplifier were coupled to a .has diminishing impedance with increasing irs complete selector, consisting of cascaded tuned circuits, instead of merely to a single tuned circuit, the nature of the curves would remain essentially similar, but the curves would be elevated to have higher ordinates,

more detunin'g being needed because of the -increa'sed damping due to the coupledcircuits. The percentage variation due to reaction would then be reduced, since the reac- 3 connected to a complete selector.

tion would not so greatly affect the coupled circuits ofthe selector. Accordingly,-when the problemliere presented is solved for a single tuned circuit it is solved for the worst ease, and is therefore also solved for the case small inductance in series with an inductance free resistance shunted by a small capacity, together with coupling means to a'following tube, is especially valuable for creating in the input circuit of the preceding tube a relatively small and constant input capacity value, as--'well for eliminating reaction from the tube. By this is meant the elimination of any. resistance component across the input of the tube, whether positive or negative. In other words, the use'of such an output circuit in place of the ordinary transformer or. re-

sistance. coupled output circuit gives to the tube an input characteristic which is essentially similar to that of a fixed'loss free condenser. -The magnitude of this equivalent condenser is small, being of the order of 20 micro inicro farads with present day receiving tubes having a grid to plate capacitance of the order of three micro micro farads' and an amplification constant of the order of 12. The capacitance value is about the same even when other tubes are used.

One important use for. such anoutput circuit is in connection with an untuned ampli fier for theamplification ofa radio signal selected by a sharply tuned selector circuit comprising a cascade arrangement of loosely con pled resonant circuits. It is'essential in such a system that the last tuned circuit be free-- to oscillate with its own natural damping characteristics in order that .the desirable selectivity characteristics of the selector be retained. It is also desirable to have the amplifier input act as a fixed capacitance in order ..that the various tuned circuits in the selector may tune alike, for'otherwise it would be necessary to make the last tuned circuit have a shaped condenser plate in order to make up for variations in the amplifier input ca- 'pacity.-'

- The application of the foregoing invention, in any of the forms shown in Figs. 1, 2, and 3, tosucha complete receiver, is illustrated in Fig. 5, referring to which it will be observed that the receiver consists first of a selector, which may be of the type described in my copending application, Ser. No.

205,935, filed July 15, 1927, and which may optionally include the improvements set forth in my copending application Ser. No.

243,790, filed December 31, 1927, audit copending application of Lester L. Jones and Jacob Y'olles, Ser. No. 403,160 filed October 29, I929. The selector is followed by an am-v plifier of fixed circuit constants, such as that described in my Patent No. 1,675,287 issued June 1-2, 1928, and in my copending application Ser. No. 205,934, filed July 15.1927.

sincev issued as Patent No. 1,770,525, and which optionally may embody the improvements disclosed in my copending applications. Ser. No. 397,633, filed-October 5, 1929, and Ser. No. 402,379-filed October 25, 192$). The selected and amplified energy is rectified in a suitable detector 30, and the resulting audio frequency energy may be' further amplified, if desired, in an audio frequency amplifier 32, after which it may be translated in an -appropriate translating device such as a loud speaker 34.

Considering the schematic wiringdiagram more in detail, it will be observed that the last tuned circuit of the selector circuit 36 acts also as the input circuit for the first tube 2 of the amplifier. Between the first tube 2 and the second tube 10 of the amplifier a coupling arrangement may be used; such as those,

described in Figs. 1, 2, and 3 of the drawing,

and which in this case is similar to the-last of these. This coupling circuit comprises an output circuit including .an inductive 1mpedance 6, a condenser 16in series therewith, and a neutraliz ng or feed forward resistance 8 arranged in parallel with the condenser 16 and a portion of'the inductance 6, and a bi filar wound coupling transformer 20 the primary of which is connected across the output circuit. As is indicated on thewiring dia' gram, the bifilar wound transformer 20 pref- 'erably' consists of separated halves or coils connected inseries and 'woundin opposite directions, in order to reduce external magnetic coupling therewith, although other coils suitably. shielded might be used. The-inductance 6 similarly may consist of two separated portions wound in opposite directions. Tube 10 has a large inductance output transformerserving to-give tube-'10 an input capacitance which rises with decreasing frequency which helps keep tube 2 reaction-' less,-besides automatically tuning the input circuit of tube 10'.

The complex output circuit described makes the tube *2 almost perfectly reactionless, and the input circuit ther'eof'acts merely as a small loss free condenser. of fixed capzicitance connected across the last tuned circuit.

36 of the selector. x

Another important use to which-my reactionless cou ling circuit may be put is for an interme iate stagein an'untuned amplifier. I refer especially to the' cascaded unvided type described in Patent No. 1,67 3,287, issued June 12, 1928, and further described in my .copending application Ser. No.- 205,934 filed July 15, 1927, since. issued as Patent No.

1,770,525, and in a copending application of.

Lester L. Jones and Jacob Yolles, Ser. No; 403,161, filed Oct. 29, 1929. 'lhedesign of this typeof amplifier is relatively simple,

starting \back at the detectortl'lbe, for this tube has at radio frequencies a relatively small and constant input capacitance and isfree from reaction. The suitably large in-' ductance in the output circuit of the last radio frequency stage therefore creates a. rising input capacitance with lower frequency characteristic in this stage, which is suitable for automatic tuning.-

If a preceding radio frequency amplifier stage is coupled directly thereto this stage is not suitable for automatic tuning over the same frequency range'because its output circuit is held nearly resonant to the various frequencies in the lower frequency portion of the range. However, with respect to fre' quencies in thehigher frequency portion of the range its output circuit is resonant to a relatively lower frequency and therefore the input circuit of the preceding stage may be. automatically tuned -to frequencies. in the higher frequency portion of the range. In general, thejfull working frequency range may be divided into as many portions as desired anda similar numberof stages proeach of which is automatically tuned to-a different one of the frequency portions. However, it is desirable to design each stage for as large a frequency range as it can efli' ciently automatically tune to, and to use onlyso many stages arranged directly in cascade as may prove necessary 'to cover the full working frequency range, because the cas caded group consists, ineffect, of only one accurately tuned stage and a remainder of less etficlent stages. If greater gain and more stages are desired in the amplifier it. is therefore preferable to have these stages automatically tuned over the full working frequency range, rather than to divide the range into smaller portions, but it then is im-' possible to cascade thestages directly together-because the necessary relation that the successive coupling circuits have successively decreasing natural frequencies cannot then he fulfilled. j I

It therefore is desirable to introduce at this point a reaction free stage an inter-' mediate linkcircuit so as to permit the further efficient use of additional automatically tuned stages in. the .multi-stage amplifier. The use of the reaction free coupling circuit herein disclosed gives to the tube preceding it. a constantcapacitance and reaction free input characteristic similar to that found in ,the detector. tube. .The design of the first cuit itself is not claimed in this application,

it being described more in detail and claimed in the eopending application of Lester L.

Jones and Jacob Yolles, Ser. No. 403.16]. filed October 29, 1929, previously mentioned. Referrim to Fig. 6, the antenna circuit. 40 is coupled to a tuned stage 4.4. of which is-coupled to a radio frequency amplifier 46. The amplifier 46 comprisesa reactionless or link stage 48 followed by two automatically tuned amplifier stages 50 in turn followed by another reactionless or link stage 52 which separates the automatically tuned stages 50 from an additional pair of automatically tuned amplifier stages 54.' The amplifier output is supplied to a detector tube 56, the rectified output from'which may, if desired, be further ainplified in an audio frequency amplifier 58.

the output of which is translated inany suitable translating device here exemplified by a loud speaker 60'.

It will be observed that the reactionless stages 48 and 52 haveoutput circuits similar to those shown in Figs. 3 and 2 of the drawing, respectively, it net-being necessary for stage 52 to be as perfectly reactionless as stage 48, because stage 52 does not react upon a sharply tuned circuit, as does stage 48. It will be understood that the illustrated output circuits may, if desired, be replaced by that shown in Fig. 1.

It is. preferred to use automatic tuning in the tube at 'a frequency higher than the hightunable selector 42, the last llf) est frequency of the working frequencv range. It therefore compensates for a tendency of the amplification to fall oil at the higher frequnecies due to the higher frequencies being shunted by the tube input capacitance. v

Returning again to the coupling circuit, as a sample of the quantitative values which maybe employed, and referring to the coupling arrangement shown in Fig. 2, and assuming that standard tubes having the following characteristics :'grid to plate. ca-

- resistance, is applicable.to a single reactionpacitance equals 3 M. M..F., amplification factor equals 13, tube conductance equals 1:300"microinhos, are used, the resistance 8 may ha re a resistance of say 2800 ohms, the capacitance It) a value of say 18 M. M. F.s, the imluctai-u-e (5 may be wound of say two 85 turn halves in series, having 240 microh. total inductance, accompanied by an inherent resistance of only about 100 ohms, while the transformer 20 may consist of two 200 turn halves in series in both its primary and secondary, and ha \'0 a total inductance of 1100 microh. .These constants aresuitable fora range of 500 to 1500 kilocycles, or say 200 to (300 meters.

Referring to the modification shown in the portion of the inductance 6 connected in shunt with the resistance 8 may have a value of sa $lt);mierol1., the remainder of the inductance 6 connected in series with the resistance 8 may have a value of say 244 microlr. while the mutual inductance between the portions of the inductance 6 may have a value of say 27'microh., the inherent resistance in inductance 6 being only about i 100 ohms, the transformer 20 meanwhile having an inductance of 1240 microh.

The stage including the following tube, or tube 1t) if arranged as an additional transition stage for perfecting the reactionlessness of tube 2, should have an output inductance 11 which may consist of'about 600 turns random wound and having an inductance of about 4.5 millihenries, assuming the tube 10 to be a standard tube of characteristics. similar to those already mentioned in the case of tube 2.

tion stages, so that the sec'ond may correctfor' resldual reaction through the first, the present invention, in so-far as it relates to the beneficial effect obtained by the provision of' a capacitance in parallel with the feed forward less stage. For example, if the link stage worked into a system of very'lo'w capacitance,

say a few M. M. F,, thercaction characteristic would haveapproximately the correct slope even without theuse of a second transition stage, but would nevertheless havethe undesirable regenerative reaction in the iniddle of the working frequency range whichis 'eliminated the use .ofthe'parallel connected capacitance.

It also is of utilityi-n an arrangement such as is shown in Fig. 6, in which the tube follow'ingthe reactionless stage only partially helps to load the output circuit thereof with afdesired corrective capacitance,

circuit.

.in series with said arranged in shun inasmuch as this tube also acts as the first tube of-a pair of automatically tunedstages, and therefore cannot have in its output circuit a sufiiciently large-inductance to act to the optimum as a second transition stage.

The circuit arrangement of my invention, the manner of applying it, and its advantages, will for the most part be apparent from the foregoing description thereof. It will also be understood that, relative to my invention as set forth in my copending application, Ser. No. 205,934 already referred to, since issued as Patent No. 1,77 0,525, the present improvements may be considered in two aspects, one of which consists in the changes made to the output circuit of the first tube, that is to say, to the shunt circuit connected in parallel with the coupling circuit, and the other of which consists in the successful introduction of transformer cou -pling in this type of circuit andfin appropriate changesin the accompanying circuits,

the transformer circuit leading to advantages previously pointed out.

It will be apparent that while I have shown and described my invention in the preferred forms, many changesand modifications may be made in the structures disclosed without departing from the spirit of the invention defined in the following claims.

I claim:

1. An amplifier stage comprising an elec-- tron emission tube and associated input and output circuits, means in said output circuit to make thegreaction through the tube regenerative throughout theworking frequency range, means to neutralize the regeneration in orderto' prevent reaction upon the input circuit, and transformerineans connected in parallel with said output circuit' forcoupling the output circuitof the tube to a succeeding circuit, said transformer means having a low resistance relative to'that of the output 2. An amplifier fstage comprising anelectron emissiontubaan inductive impedance in the output circuit-of said tube, a resistance ductance, a capacitance thflshid resistance, and additional mean] ,dr coupling the output circuit of the tube to a, succeeding circuit;

3. An amplifier-stagecomprising an elec tron emission tube, an inductive impedance in the output circuit of said tube, a resistance in serieswit-h-said inductance, a capacitance arranged in shunt with all of said resistance and a portion of said inductance, and additional means for coupling the output, circuit of the tubeto a succeeding circuit. 5

4. A 'reactionless amplifier stage' comprisingan electron emission tube, an inductive impedance in. the out-put circuitof said tube 1n order to make its reaction regenerative over the working frequency range, a resi'stance in se'rieswith said inductance for causing a feed forward reaction opposed to parent input capacitance with frequency designed to correct the-residual reaction in the first transitionstage, and a bifilar-o'r equivalent closely coupled transformer for. cou-. =pling the first and second stages in order to transfer the input capacitance of the second stage to the output circuit of the first stage; i

6. A reactionless amplifier, comprising a first electron emission tube, an inductive impedance in the output ofsaid tube, a resistance in series with said inductance, a'capacitancearranged in shunt with said resistance, a second electron emission tube, an

output circuit therefor arranged to give the input circuit thereof -a decreasing apparent capacitance with increasing frequency, and additional means for coupling the output circuit of the first tube to the input circuit of the second tube. I

7. A .radio receiving circuit comprising a selector having variable circuit constants, a

v the reaction of the first amplifier tube revacuum tube amplifier havi 'ng fixed circuit constants, and means coupling said amplifier to said selector comprising means to make generative throughout the working frequency range, means to neutralize the consequent regeneration in order to prevent 'reaction by the amplifier upon the selector, and bifilar transformer means for coupling the output circuit of the first amplifier tube tobthe input circuit of the second amplifier tu e. .l

8. A radio receiving circuit comprising a selector, a cascade 'vacuum tube amplifier,

. and means coupling said amplifier to said selector comprising the first tube of said am.-

. plifier, an inductive impedance in the output circuit of saidfirst tube, a resistance in series with said inductance, a capacitance arranged in shunt with said resistance, and means coupling the output circuit of the first tube to the input circuit of the next tube of the amplifier. 1

9; A' radio receiving circuit comprising a selector, 'a' cascade vacuum tube amplifier, and means coupling said amplifier to said selector comprising thefirst tube of said amplifier', an inductive impedance in the output circuit of said first tube, a resistance in series with said inductance, a capacitance arranged in shunt with all of said resistance and a transformer,

means for coupling the output circuit ofthe first tube to the input circuit of the next tube of the amplifier.

10. A radio receivin circuit comprising a selector having variab e circuit constants, a

cascade vacuum tube amplifier having fixed circuit constants, and means coupling said amplifier to said selector comprising the first tube of said amplifier, an inductive impedance in the output circuit of said first tube in order to make its reaction regenerative over the working frequency range, a resistance in series with said inductance for causing a feed forward reaction opposed to the regenerative feed back reaction, a capacitance arranged in shunt with said resistance, and means coupling the output circuit of the first tube to the input circuit of the ,next tube of the amplifier.-

, 11. A radio receiving circuit comprising a selector having variable circuit constants, a cascade vacuum tube amplifier having fixed circuit constants, and means coupling said amplifier to said selector comprising the first portion of said inductance, and additional 7 tube ofsaid amplifier, an inductive impedance in the output circuit of said first tube in order to make its reaction regenerative over the working frequenc range, a resistance in series with said in uctance and a capacitance arranged inlshunt with said resistance for causing a feed forward reaction opposed to the regenerative feed back reaction in order to prevent reaction by said amplifier upon said selector, and additional transformer means for coupling the output circuit of the first tube to the input circuitrof the next tube of the amplifier.

12. A radio receiving system comprising first and second vacuum tubes and coupling means therefor comprising a transformer and a shuntcircuit arranged in parallel with the primary of said transformer, said shunt circuit consisting of a series combination of a capacitance and an inductance, and a resistance connected in parallel with said capacitance.

13'. A radio receiving system comprising first and second vacuum tubes and coupling means therefor comprising a very closely coupled transformer and a shunt circuit arranged in parallel with the primary of-said said shunt circuit consistin of 'a series combination of a capacitance and an inductance, "and a resistance connected in parallel with saidcapacitance and a portion of said inductance.

14. A radio receiving system comprising a selector, a cascade vacuumtube amplifier, means coupling the first and'second vacuum tubes of the amplifier comprising a bifilar wound transformer and a shunt circuit arranged in parallel with the primary of said transformer, said shunt circuit including a series combination of a capacitance and an inductance, and a resistance connected in series combination of a capacitance and an inductance, and a resistance connected m parallel with said capacitance, and means coupling the second and third vacuum tubes .of theam lifierarran ed to prevent residual reaction t rough the fier on the selector. p 15. A radio receiving, system comprising a first tube by the ampli- Selector having variable circuit constants in' parallel with said capacitance.

16. A radio receiving-system comprising a selector having variable circuit constants in order to permit tuning thereof, ancascade vacuum tube amplifier having fixed circuit constants, and means-coupling the'first and second vacuum tubes of the amplifier com-' prising a transformer and a shunt circuit arranged in parallel with the primary of said transformer, said shuntcircuit including a series combination of 'a' capacitance and an inductance, and a capacitance and inductance free resistance connected in parallel with said capacitance and a portion of said inductance.

' 17.' A radio receivingsystemcomprising a selector having variable circuit constants in order' to permit tuning thereof, a cascade vacuumtube amplifier having fixed circuitv constants, means including a tuned circuit for coupling the-selector to .the first tubejof the amplifier, and means cou ling the first and second tubes of the ampli er comprising a bifilar transformer and a shunt circuit arranged inparallel with the primaryof said transformer, said shunt circuitincluding a series combination of a-capacitance and-an inductance, and a capacitance and inductance free resistance connectedin parallel with said capacitance and a portion of said inductance. 18. A reactionless amplifier comprising a first electron emission tube, an inductive impedance in the outputof said tube, a resistance in series with said inductance, a capaci- ;tance arrangedin shunt with said resistance,

cuit thereof a decreasing apparentcapacitance with increasing frequency, anda bifilar transformer or equivalenticlosely coupled transformer means for coupling the output circuit of the first tube to the input circuit of the second tube.-

19. A radio receiving circuit comprising a selector, a cascade vacuum tube amplifier, and means coupling said amplifier to said selector comprising thefirst two stages of said amplifier, the first stage having anoutput circuit including an inductive impedance, a resist-g ance inseries with. said inductance, and a capacitance arranged in shunt-with said resistance, the second stage having an output, circuit arranged to give the input circuit thereof a decreasing capacitance characteristic with increasing frequency, and means coupling the output circuit of the first tube stage to the input circuit of the next stage of the-amplifier.

20. A radio receiving circuit comprising a selector, a cascade vacuum tube amplifier, and

means-coupling said amplifier to said selector comprising the first two stages of said amplifier, the first stage .having an output circuit including an inductive impedance, a resistance in series with said inductance, and a capacitance arranged'in shunt with said resistance, the second stage having an output circuit arranged to give the input circuit thereof a decreasing. capacitance characteristic with increasing frequency, and a bifilar transformer or equivalent'closely coupled transformer means coupling the output circuit of the first tube stage'to the input circuit of next stage of the amplifier. I

'21. A reactionless amplifier comprising a ,1 vacuum tube, an inductance in the output circuit thereof arranged to make the reaction of the tube regenerative.- a resistance in series with said inductance for opposing the regenerative reaction of the tube, said inductance and resistance being greatly increased in magnitude over thevcorrectvaluefor making the tube reactionless in order toincrease the gain therein, and means arranged to prevent resi -v dual reactions through the tube caused by the the said increase in the output impedance thereof.

' 22. A; reactionless amplifier comprising a vacuum tube, an inductance in the output circuit thereof arranged to. make the reaction of the tube regenerative, a resistance in-s'eries with said inductance for opposing the regenerative reaction of the tube, said inductance and resistance being greatly increased in magnitude'over' the correct value for makcaction of the tube regenerative, a resistance in S6I1GS with'said inductance for opposing the regenerative reaction of the tube," said. inductance and resistance being-increased in magnitude to about twice the correct value for making the tube reactionless in order. to iii- I vcrease the gain therein, and a second vacuum tube coupled to the output circuit of the first and arranged to prevent a'residual'reaction through the first tube-caused by the said doubling of the output impedance thereof.

'ingthe tube reactionlessin order to increase the gain therein, and acapacitance arranged in parallelwith the said resistance in order I to prevent a residual reactionthrough the tube caused by the said increase in theoutput. v s fimpedance thereof.

. a second-electron emission tube, an output circuit therefor arranged to give' the input'cir- 24. 'A reactionless a 'plifier comprising a. first vacuum tube, an inductance in the output circuit thereof arranged to make the reaction of the tube regenerative, a resistance in series with said inductance for o posin the regenerative reaction of the tu e, sai

inductance and resistance being greatly increased in magnitude over the correct value for making the tube reactionless in order to increase the gain therein, a second vacuum tube coupled to the output circuit of the first and arranged to prevent a residual reaction through the first tube, and a capacitance arranged in parallel with the aforesaid resistance in order to prevent an additional residual reaction through the first tube, said increase the gain therein, a second vacuum tube coupled to the output circuitiof the first and arranged to prevent a residual reaction through the first tube, and a capacitance 'arranged in arallel with the aforesaid resistance in ord ier to prevent an additional residual reaction through the first tube, said residual reactions bein caused by the said doubling of the output-impedance of the first tube.

26. A radio receiving circuit -comprising a selector tunable over a given frequency range, a reactionless am lifier comprising a first vacuum tube, an inductance in the output circuit thereof arranged to make the reaction of the tube regenerative, a resistance in series with said inductance for opposing the regenerative reaction of the tube, said inductance and resistance being increased in magnitude to about twice the correct value for making the tube reactionless over the whole frequency range in order to increase the gain in the. tube, a second vacuum tube coup ed to the output circuit of the first and arranged to prevent a residual reaction throu h the first tube, and a capacitance arranged in' arallel with the aforesaid resistance 1n or er to prevent an additional residual reaction through the first tube over a portion of the frequency range, said residual reactions being caused by the said doubling of the output impedance of the first tube.

Signed at New'York in the county of New York and State of New York this 2nd day of October A .=-D. 1929.

LESTER L. JONES.

uctance in the out- 

